This investigation aims to solve the three-dimensional structure of scolexin, an infection- induced insect coagulation protein, and compare it to similar mammalian proteases in an effort to provide insight into the origins of blood coagulation and immunity. Biochemical investigation of scolexin's proteolytic and sugar-binding activities described herein may also deepen our understanding of how mammalian proteases of coagulation and immunity are regulated. These aims will be pursued with the following research design: 1) Overexpress scolexin in bacterial and recombinant baculovirus systems. 2) Crystallize the purified scolexin and determine its three- dimensional structure using X-ray crystallography. 3) Investigate the proteolytic processing (and possible activation) of scolexin using epidermal extracts and/or proteases of appropriate specificity. 4) Characterize the glycosylation of scolexin using both glycosidases and enzyme-conjugated lectins. 5) Directly measure and characterize scolexin' s sugar-binding activity using titration microcalorimetry. 6) Assay scolexin for proteolytic activity using a variety of assay systems and substrates.